The present invention relates to an engine intake control mechanism that has a throttle valve and a choke valve for controlling the quantity of an air/fuel mixture inducted into an internal combustion engine. In particular, the present invention relates to an engine intake control mechanism in which the throttle valve is rotated to a cold-starting position in association with the choke valve at the time of cold-starting, and the choke valve is automatically returned to its original opened position after the engine is started.
In the operation of a fuel/air mixing device, such as the carburetor of an internal combustion engine that powers a portable power working machine, for example, a chain saw, it is required when the engine is first started, especially in cold weather, that a fuel/air mixture of relatively rich composition be fed to the engine since the vaporization of fuel is poor when the engine is cold. Therefore, a choke valve is positioned upstream from the venturi portion of the air inlet passageway of the carburetor and is brought to its closed position by rotating the choke to the cold-starting position at the time of cold-starting, thereby greatly reducing the quantity of inducted air and at the same time increasing the negative pressure of the venturi portion of air inlet passageway, thus increasing the quantity of fuel drawn from the fuel supply by the air flow.
For an engine intake control device provided with such a choke valve, a previously known auto-return type device, as shown in Japanese Patent Unexamined Publication S52-104642 (U.S. Pat. No.4,123,480), is constructed such that at the time of cold-starting, the throttle valve is rotated to the cold-starting position xe2x80x94a slightly rotated position in the opening direction from its idling position xe2x80x94in response to the closing movement of the choke valve. After the engine starts, the throttle valve is actuated so as to increase the opening degree thereof, thereby enabling the choke valve to automatically return to its original opened position.
In a portable power working machine, such as a chain saw, there is previously known a so-called top handle-type power working machine, examples of which are shown in Japanese Patent Unexamined Publication H5-195891 and Japanese Patent No. 2931234. Such machines have a top handle that is attached to the top surface of the main body housing for the internal combustion engine and a side handle that is attached to the sidewall of the main housing. A lock-canceling lever for canceling a lock device, which is designed to lock the throttle valve in its idling position, protrudes from the top surface of the top handle. A throttle lever for rotating the throttle valve is attached to the underside of the front end of the top handle. A recoil starter handle for starting the engine protrudes upwardly from the left sidewall of the main housing.
If the aforementioned conventional auto-return type engine intake control device were to be used in the aforementioned portable power working machine of the top handle type, the following problems would be presented:
At the time of cold-starting of the power working machine, especially when the operator is in unstable position such as working on a tree, the operator is required first to manipulate the choke controlling element, such as thumbscrew or lever attached to the main housing, to rotate the choke valve from its opened position to the partly closed, cold-starting position. Then, the user needs to grip the top handle with his right hand and at the same time to pull the recoil starter handle with his left hand so as to start the engine. When operator grips the handle, the lock canceling lever that protrudes from the top of the top handle is inevitably squeezed and caused to rotate in the lock-canceling direction. Also, the operator may inadvertently touch the throttle valve. As a result, the throttle lever is caused to rotate in the direction to increase the opening degree of the throttle valve. Hence, the choke valve is caused to return from the coldstarting position to its original opened position, thereby raising the problem that the cold-starting performance of the engine would be deteriorated because the intake passageway of the carburetor cannot be sufficiently constricted for enabling the cold-starting.
The present invention is directed to solving the aforementioned problems. It is, therefore, an object of the present invention to provide an engine intake control mechanism which is constructed such that the throttle valve can be rotated so as to bring it into the cold-starting position in response to the closing movement of the choke valve at the time of cold-starting and then, with the throttle valve locked in the cold-starting position, the choke valve is retained at the cold-starting position even if the throttle valve is actuated by the operator to increase the opening degree of the throttle valve. In addition, when the throttle lever that has been once gripped is released to thereby enable the throttle valve to return to its closed position, the choke valve is allowed to automatically return to its original position. By meeting the foregoing objectives, the engine intake control mechanism is well suited for use in a portable power working machine of top handle type.
With a view to attaining the aforementioned object, there is provided, according to the present invention, an engine intake control mechanism that includes a throttle valve and a choke valve, which are positioned in an intake passageway of an air/fuel mixing device adapted to be mounted on an internal combustion engine. A first throttle control lever is coupled for rotation with a rotatable shaft of the throttle valve. A second throttle control lever is rotatable about an axis of the rotatable shaft of the throttle valve. A throttle return spring urges the throttle valve to rotate in the closing direction thereof. A coupling spring links the first throttle control lever to the second throttle control lever to enable the first throttle control lever and the second throttle control lever to rotate together. A choke control unit is coupled for rotation with a rotatable shaft of the choke valve. A choke return spring urges the choke valve to rotate in the opening direction thereof.
The choke control unit is arranged such that: (1) when the choke control unit is rotated together with the choke valve so as to move the choke valve into a cold-starting position, the first throttle control lever together with the throttle valve and the second throttle control lever are caused to rotate in response to the rotation of the choke control unit so as to position the throttle control valve in a cold-starting position; (2) the choke control unit and the first throttle control lever are interlocked with each other so as to retain the cold-starting positions thereof against the biasing forces of the choke return spring and of the throttle return spring; and (3) when the first throttle control lever is further rotated from the interlocked state in a direction to increase the opening degree of the throttle valve, the first throttle control lever is disengaged from the choke control unit and at the same time the choke control unit is engaged with the second throttle control lever, thereby interlocking the choke control unit with the second throttle control lever at the cold-starting position.
It is preferred in the engine intake control mechanism according to the present invention that the coupling spring be a torsion coil spring, which is interposed between the first throttle control lever and the second throttle control lever.
In a preferred embodiment of the present invention, the first throttle control lever is provided with a first throttle side engaging portion, which is arranged to be engaged with the choke control unit, and a press-engaging portion, which is arranged to be releasably engage the second throttle control lever by the biasing force of the coupling spring. The second throttle control lever is provided with a second throttle side engaging portion which is arranged to be engaged with the choke control unit.
In another preferred embodiment of the present invention, the choke control unit is provided with a first choke side engaging portion, which is arranged to be engaged with the first throttle side engaging portion of the first throttle control lever, and a second choke side engaging portion, which is arranged to be engaged with the second throttle side engaging portion of the second throttle control lever. In a further preferred embodiment of the present invention, the choke control unit is provided with a first choke control lever, which is arranged to be rotated integral with the rotatable shaft of the choke valve, and a second choke control lever, which is arranged to be rotated about an axis of the rotatable shaft of the choke valve. The second choke control lever is provided with the first choke side engaging portion and the second choke side engaging portion, the first choke control lever being urged by means of the choke return spring and via the second choke control lever to move in the direction to open the choke valve.
Preferably, the choke return spring is a torsion coil spring, which is interposed between a main body of the air/fuel mixing device and the second choke control lever.
When an engine intake control mechanism constructed as described above and according to the present invention is used with an internal combustion engine of a top handle type portable working power machine, the operator first manipulates the choke controlling member, such as a thumbscrew or lever attached to the main housing of the machine, so as to rotate the choke control unit and the first and second choke control levers against the forces of the choke return spring and the throttle return spring and to thereby bring the choke valve and the throttle valve into their cold-starting positions.
In particular, the choke valve is caused to rotate with the choke control unit, thereby moving it from its normal open position to the cold-starting, nearly closed position. At the same time, the choke control unit engages the first throttle control lever so as to rotate the first throttle control lever, against the bias of the throttle return spring, from a position for idling of the engine into the cold-starting position, in which the throttle valve is slightly opened from the idling position.
As the first throttle control lever is moved to the cold-starting position, the throttle valve rotates with the first throttle control lever so as to move it into the cold-starting position. At the same time, the second throttle control lever, which is linked by the linking spring, such as a torsion coil spring, to the first throttle control lever, is also rotated so as to bring it into the cold-starting position. Ultimately, the choke control unit and the first throttle control lever are interlocked with each other so as to retain the cold-starting positions thereof against the biasing forces of the choke return spring and the throttle return spring.
When the choke is thus set, the operator grips the top handle of the machine with his right hand and pulls the recoil starter handle with his left hand to start the engine. When the operator grasps the top handle, he is apt to also move the throttle lever attached to the top handle, which causes the first throttle lever to rotate, via a linkage member such as a cable or a link rod, from the locked state of the throttle valve in a direction to increase the opening degree of the throttle valve from the cold-starting choke position.
When the first throttle control lever moves from the cold-starting position as mentioned above, the first throttle control lever is permitted to disengage from the choke control unit. However, simultaneously with the disengagement, the choke control unit engages the second throttle control lever, so that the second throttle control lever and the choke control unit become interlocked with each other so as to retain the cold-starting position of the throttle valve. Even if the throttle lever is forced to rotate toward open from the cold-starting position, as described above, the second throttle control lever and the choke control unit remain in their interlocked state. The first throttle control lever, however, is able to rotate against the biasing force of the coupling spring.
As a result of these operations, the engine can be started and brought into a state in which combustion will be sustained and the engine speed increased, thus completing a cold start.
Thereafter, when the operator releases the throttle lever, the first throttle control lever is forced to rotate by the biasing forces of the throttle return spring and the coupling spring, in a direction to close the throttle valve. At that point, the throttle valve the second throttle control lever return to the idling positions. Thereupon, the choke control unit is released from its locked state, thereby enabling it to return at the urging of the choke return spring, to its original normal rest position in which the choke valve is open. The choke-actuating member is also permitted to return to its original position.
Subsequently, when the throttle lever is gripped again by the operator under the condition wherein the chokeactuating member and the choke control unit reside in their normal rest positions, the first throttle control lever as well as the second throttle control lever are forced to rotate, without being engaged with the choke control unit, in the direction to open the throttle valve to a suitable extent, depending on the magnitude of the rotation of the throttle lever.
With the engine intake control mechanism of the present invention, the throttle valve is at the time of cold-starting be rotated in response to the closing movement of the choke valve so as to bring it into the cold-starting position thereof, and at the same time, even if the throttle valve is actuated so as to increase the opening degree thereof, the choke valve can be retained at the cold-starting position. Thereafter, only when the throttle valve is actuated to return to its original closed position the choke valve is automatically returned to its original opened position. Therefore, the engine intake control mechanism of the present invention is well-suited for use in top handle type portable power working machines, inasmuch as it improves the cold-starting operation of such machines.
For a better understanding of the present invention, reference may be made to the following description of an exemplary embodiment, taken in conjunction with the accompanying drawings.